A quadrilateral is a four-sided polygon, like a square, rectangle, or rhombus. The computer screen you are looking at right now is probably in the shape of a quadrilateral.
The quadrilateral — like the triangle and circle — are shapes you'll learn about in geometry. Quadrilaterals include more than one type of shape, but all quadrilaterals have four sides. The most common type of quadrilateral is the square, but rectangles and rhombuses are quadrilaterals too. Quadrilaterals are also called quadrangles and tetragons. When you see the word quadrilateral, think "four sides".
